Hydraulic fracturing, also known as hydrofracturing and fracing, is a commonly used technique in the removal of hydrocarbons from a reservoir. Hydraulic fracturing increases the pressure in a rock formation until tensile strength or shear strength is exceeded to create fractures in the rock formation. The newly created fractures can provide passageways through which the hydrocarbons can travel to a wellbore or well. The newly created fractures can also increase the area of the reservoir that can be accessed by a single wellbore. Absent the newly created fractures in the rock formation, the permeability of the rock formation can be too low to allow hydrocarbons to be recovered at an economic rate.
Hydraulic fracturing involves injecting a fracturing fluid into the wellbore to a section of the wellbore that is exposed to the rock formation. The section is exposed to the rock formation either because there is no well casing at the depth of the rock formation or because holes have been intentionally made in the casing adjacent to the rock formation. The fracturing fluid is injected at a rate that is sufficient to increase local stresses to a value in excess of the strength of the rock formation. After the local stresses exceed the tensile or shear strength of the rock formation, fractures will form in the rock formation. Continuing to inject the fracturing fluid at a rate which exceeds the rate at which fluid can flow through the permeable portions within the rock formation will typically extend the fractures further into the formation.
When a fracture is sufficiently wide to allow proppants to flow into the fracture, proppants in the fracturing fluid are deposited in the newly created fractures during injection of the fracturing fluid. The proppants are meant to hold the newly created fractures open so that hydrocarbons can more easily flow to the wellbore. After the fracturing process is completed, the fracturing fluid is removed by flowing or pumping it back out of the wellbore so that the fracturing fluid does not block the flow of hydrocarbons to the wellbore. Although the fracturing fluid is removed, the proppants, which are typically solid particles, remain and can slow down or partially impede the flow of hydrocarbons to the wellbore (e.g., relative to flow through a completely open fracture of the same width).
Thus, the hydrocarbon industry is constantly searching for improved proppants.